672 E. O. ULRICH REVISION OF THE PALEOZOIC SYSTEMS 



tliis limestone rests on the upper Cambrian I^olichncky shale and hitherto 

 has always been described as a sparingly cherty representative of the 

 Knox dolomite. It is a great valley-maker in this region and very thick. 

 I have measured it at only one place, namely Jonesboro, Tennessee, 

 where the formation, though incomplete above, reaches a thickness of 

 about 1,850 feet. The total thickness in this vicinity is probably 400 feet 

 more, or in all about 2,250 feet. As a rule the early Stones Kiver 

 Mosheim limestone succeeds it. 



Gastropods allied to Madurea oceanea and M. a/finis, and to Seelya — 

 types so far wholly unknown in the typical Knox or, indeed, in any 

 Ozarkian formation — occur at intervals in the Jonesboro section to 

 within 400 feet of the top of the underlying ^olichucky. The upper 

 400 feet of the limestone very commonly contains Ceratopea IceitM and 

 less frequently other gastropods and cephalopods. Mr. Arthur Keith 

 found this same fauna east of Knoxville in beds referred by him to the 

 upper Knox. As a rule, the fossils are silicified and weather out free 

 from the limestone matrix. 



As developed in the valley beginning in the north at Wytheville, Vir- 

 ginia, and extending thence southward to Greeneville, Tennessee, these 

 Canadian limestones are readily distinguished from the dolomitic main 

 Copper Ridge division of the typical Knox by the relatively small amount 

 of chert in them. Cherty bands occur at various horizons in the series, 

 but they form a conspicuous feature of the weathered surface only in 

 the upper 200 or 300 feet and again some 250 to 500 feet above the base. 

 These cherts, however, are quite different from the massive, hard white 

 chert of the Copper Ridge. As a rule, the Canadian chert is often 

 porous; other layers are dense and brittle, platy, mottled, often black, 

 occasionally scoriaceous, and most of it breaks easily under the hammer. 

 Another characteristic is that it is nearly always associated with porous 

 sandstone. 



As this formation is a stratigraphic and lithologic unit, and distinct 

 from all others now recognized by name in the Appalachian Valley, the 

 term Jonesboro limestone is here proposed for it. 



Canadian deposits were observed locally in the counties of McMinn, 

 Bradley, and Polk in southeastern Tennessee, and near Ringgold, Geor- 

 gia. These, however, are thin — at a maximum perhaps less than 250 

 feet — and underlain by Copper Ridge chert. They are fossiliferous. but 

 I have not observed the characteristic species of the Ceratopea fauna 

 in the collections made. On this account it is believed they represent 

 some other age of the period. 



